Avalanche Forecast

Issued: Dec 23rd, 2011 8:43AM

The alpine rating is high, the treeline rating is high, and the below treeline rating is considerable. Known problems include Wind Slabs, Storm Slabs and Persistent Slabs.

Avalanche Canada jlammers, Avalanche Canada

Summary

Confidence

Fair - Intensity of incoming weather is uncertainfor the entire period

Weather Forecast

Saturday: 20-30cm of snow - moderate to strong southwest winds - freezing level at 1000mSunday: 8-15cm of snow - moderate southwest winds - freezing level at surfaceMonday: moderate snowfall - Moderate winds from the south - freezing level at surface

Avalanche Summary

Limited observations at this time. Expect widespread natural avalanche activity throughout the weekend for forecast wind and snow.

Snowpack Summary

Earlier this week the forecast region got slammed by snow, wind and fluctuating freezing levels. Including the 20cm that fell on thursday night, the southern part of the region has received over a meter of new snow over the past week (Kasiks, Terrace areas). Locations to the north are seeing less (Stewart up to 60cms). This new snow has been blown around by extreme-strong southwest winds creating stiff wind slabs on lee slopes. The winds have switched from the SW to the NW. This switch was short lived through Wednesday, but may have formed new wind slabs on SE - S facing slopes. This makes the wind slab problem even trickier to predict. In addition to the more obvious direct-action storm instabilities that are expected with the forecast weather, local avalanche professionals have some other concerns: Surface hoar that formed during the winter solstice sits approximately 30cm below the surface and will become more reactive with more wind and snow. As well, the crust-facet combo (extends up to alpine elevations in the south and around 1000m in the north) from the early december dry-spell sits about 135cm below the surface and has not gone away . Any avalanches on this layer would be highly destructive and is probably waiting for the right load or trigger. The mid and lower snowpack are settled out and strong. Snowpack depths in the Kasiks, Terrace areas are reaching the 300cm mark. Further north Smithers, Bear Pass depths are ranging from 180-250cms.

Problems

Wind Slabs

An icon showing Wind Slabs
Strong winds will form large wind slabs on cross-loaded and lee slopes. They will be touchy and destructive in many parts of the region.

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Storm Slabs

An icon showing Storm Slabs
Heavy snowfall amounts have created and will continue to create storm slabs at all elevations.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

An icon showing Persistent Slabs
The crust that developed during the early December dry spell may awaken with increased loads or a significant trigger (cornice fall, trenching sled track). Avalanche activity on this layer would be highly destructive.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 5

Valid until: Dec 24th, 2011 8:00AM

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